SUMMARY: zCall is a variant caller specifically designed for calling rare single nucleotide polymorphisms (SNPs) from array-based technology. This caller is implemented as a post-processing step after a default calling algorithm has been applied. The algorithm uses the intensity profile of the common allele homozygote cluster to define the location of the other two genotype clusters. We demonstrate improved detection of rare alleles when applying zCall to samples that have both Illumina Infinium HumanExome BeadChip and exome sequencing data available. AVAILABILITY: http://atguweb.mgh.harvard.edu/apps/zcall CONTACT: bneale@broadinstitute.org SUPPLEMENTARY INFORMATION: Supplementary data is available at Bioinformatics online.